1. Field of the Invention
The present invention relates to an apparatus for feeding electronic components such as semiconductor chip components to a mounting instrument, especially to said apparatus for feeding electronic components in which a plurality of tape cassettes mounted laterally on a slide base move on a slide platen.
2. Prior Art
One of the typical designs of the conventional electronic component feeding apparatus includes cassette bases for carrying a plurality of tape cassettes laterally oriented, and a slide platen for moving the cassette bases along its longitudinal direction. In this design, conventional ball-screw (ball-thread) mechanism is adopted for moving a selected cassette base to a position for component feeding.
However, the ball-screw mechanism had its limitation in moving the cassette bases with optimal high speed.
Then, the speed of moving the cassette base was improved by the introduction of linear motor as a driving mechanism inserted between the cassette base and the slide platen (Japanese patent laid-open publication No. Sho 61-239696).
The linear motor of the aforementioned development comprises a pair of stationary members attached to the slide platen and a moving member attached to the bottom surface of the cassette base, and is configured such that the moving member is sandwiched between the two stationary members in the pair. The stationary member consists of a plurality of magnets aligned along the longitudinal direction of the slide platen, and the moving member consists of a core made of magnetic material and coils wound around the core for cooperating with the magnets.
Although the high-speed transportation of the cassette base was achieved by the introduction of linear motor described above, the current electronic component feeding apparatus still has another issue to be taken care of. That is, the system is not optimized for handling the variation of the load of the cassette base (the total weight of the cassette base), as the linear motor is driven by so called direct-drive mechanism.
More specifically, the linear motor is not equipped with an acceleration/deceleration mechanism using gears and the like, thus making it impossible to adjust to the variation of the load of the cassette base.
As a result, a constant control gain is used in the circuitry controlling the operation of the linear motor regardless of the load of the cassette base. Thus, when the gain is adjusted to a maximum load for attaining fast setting time of the cassette base to a position for component feeding, the motor may subject to an abnormal vibration at a minimum load condition. Likewise, when the gain is adjusted to a minimum load for preventing the abnormal vibration of the motor, the position setting at the maximum load condition suffers from excessive undershooting and takes more time than desired before settling at the position for component feeding.
So far, the solution to the problem described above is to set the gain at a point somewhere in the middle of the maximum and minimum load conditions. Though this could prevent extreme cases of the problems described above, the operation still suffers from the motor vibration at a minimum load condition and the slow position setting at a maximum load condition, resulting in a longer setting time.
What are needed are an apparatus and a method for feeding electronic components in which the cassette base is transported by the linear motor with a proper control gain adjusted to respective load weight of the cassette base.
The apparatus for feeding electronic components of the present invention includes, as shown in FIG. 3, at least one unit base 12 capable of carrying at least one component feeding unit 13, a slide platen 11 for sliding the unit base 12 thereon, and a linear motor 14 comprising at least one stationary member 47a, 47b mounted on the slide platen 11 through a supporting base 44, 45 for each of the stationary members 47a, 47b and a moving member 48 mounted on the unit base 12, which is used to move the component feeding unit 13. The apparatus also includes, as shown in FIG. 5, a motor driver 61 for driving the linear motor 14, a memory device 66 for storing data for controlling the linear motor 14, and a control device 67 for controlling the motor driver 66 using the data stored in the memory device 66, in such a way that the control device 67 adjusts the data for controlling the linear motor 14 based on a load weight of the unit base 12 carrying the component feeding units 13. In this configuration, the component feeding units 13 mounted on the unit base 12 moves to a predetermined position for feeding the electronic components stored in the component feeding unit, under the control of the control device 67 using the data for controlling the motor 14, which is adjusted based on the load weight of the unit base 12. Although the load weight of the unit base 12 may vary depending on the load of the component feeding units 13 which the unit base 12 carries at a certain time during the production operation, a proper operation of the linear motor 14 is assured as the data for controlling the motor 14 is adjusted based on the load weight of the unit base 12 at that time.
Furthermore, the method of feeding electronic components of the present invention utilizes, as shown in FIG. 3, at least one unit base 12 capable of carrying at least one component feeding unit 13, a slide platen 11 for sliding the unit base 13 thereon, and a linear motor 14 comprising at least one stationary member 47a, 47b mounted on the slide platen 11 through a supporting base 44, 45 for each of the stationary members 47a, 47b and a moving member 48 mounted on the unit base 12, which is used to move the component feeding unit 13. The method includes, as shown in FIG. 5, moving the component feeding units 13, carried by the unit base 12, based on the data for controlling the linear motor 12 stored in a memory device 66, in such a way that a control device 67 adjusts the data for controlling the linear motor 14 based on a load weight of the unit base 12 carrying the component feeding units 13. As described above, this method assures a proper operation of the linear motor 14 by adjusting the data for controlling the linear motor 14 based on the load weight of the unit base 12.
In an embodiment of the present invention, the motor driver 61 includes, as shown in FIG. 5, a position control unit 63 for receiving driving command for the linear motor 14, a velocity control unit 64 for receiving output signal from the position control unit 63, and an electric current control unit 65 for receiving output signal from the velocity control unit 64 and for feeding output signal to the linear motor 14. The data for controlling the linear motor 14, which is adjusted based on the load weight of the unit base 12, may be any form of control loop gain of a feed back system, such as the ones shown in FIG. 5 for the control units. In particular, a velocity loop control gain of the velocity control unit can be used as the data which is adjusted based on the load weight of the unit base 12.
In other embodiment, the data for controlling the linear motor 14 is obtained from the total weight ratio to motor weight (inertia ratio) J, which is obtained from the load weight of the unit base 12 carrying the component feeding units 13. The load weight is obtained from thrust force, which is obtained from the electric current of the linear motor 14 during a tuning operation. The tuning operation is performed by moving the unit base 12 for a predetermined distance while the unit base 12 carrying the component feeding units 13 moves from a home position to the position for component feeding. The tuning operation may be performed at the time of system activation by turning on the power switch, supplying electronic components, or changing NC parameters.
The apparatus and the method for feeding electronic components of the present invention enable the adjustment of the control parameters of driving the linear motor based on the change in the load weight of the unit base carrying the component feeding units while it is being moved. Thus, it is possible to attain proper motor operation without abnormal vibration or slow setting to the position for component feeding, resulting in a large improvement in the stability of operation of the unit base carrying the component feeding units.
Furthermore, the number of the tuning operations decreases as it is performed at the moment when supposedly most significant changes in the load weight of the unit base occur, such as the time of system activation and supplying electronic components to the unit base. Still furthermore, the electronic component mounting process does not have to be halted during the tuning operation as it is performed while the unit base moves from a home position to the position for component feeding, resulting in a much improved work efficiency.